The invention generally relates to magnet design and fabrication, and in particular the invention relates to a permanent magnet radial magnetizer which has a lower magic hemisphere and an upper magic hemisphere with a gap there between in which a ring shaped workpiece can be radially magnetized.
In the state of the art, radially magnetized rings are used for applications such as traveling wave tubes, klystrons, and the like. Typically, high coercivity permanent magnets of toroidal or disk-like shape are difficult to magnetize radially. The difficulty arises for toroidal magnets because the thickness of the magnet is too large thus preventing sufficient flux from flowing into the toroidal hole which can then spread radially outward. This problem is discussed in U.S. Pat. No. 4,592,889 and in a U.S. Government Technical Report DELET-TR-84-5 ERADCOM 1984.
U.S. Pat. No. 4,592,889 further describes a method and apparatus for pressing and aligning radially oriented toroidal magnets. The prior art magnetizer described in U.S. Pat. No. 4,592,889 includes a magnetic flux producing means having two opposing electrical coils, two electrical insulators for embedding the coils, and a yoke member for holding a workpiece to be magnetized radially.
One problem with the prior art magnetizer is that it requires a relatively high capacity power supply.
As noted in the above report, an aligning field of 2-4 kilooersteds (kOe) is sufficient for alignment of the constituent magnetic powders during fabrication. However, a larger field is required to achieve complete magnetization. In the prior art magnetizer, described in U.S. Pat. No. 4,592,889, a high-current, opposing-coil impulse-magnetizer was used to provide nearly 10 kOe of field. However, a significant drawback of this prior art magnetizer is that it requires a current source of thousands of amperes (amps) capacity, as well as two opposing electrical coils of a plurality of winding which must be embedded in a relatively strong electrical insulator to hold the coil structure together. A metal case must also be used to provide additional strength and safety to the coil structures.
Accordingly, it is an object of the present invention to provide a permanent magnet radial magnetizer that produces sufficient flux to radially magnetize a toroidal ring magnet and which does not require a high-capacity power supply.
This and other objects of the invention are achieved by a compact permanent magnet structure of magnetically opposing hemispheres with a central cavity to produce a uniform high field within the cavity for radially magnetizing toroidal ring magnets. A hemisphere is a hemispherical flux source. Briefly, a permanent magnet radial magnetizer according to the principles of the invention includes a lower hemisphere having an axis, an upper hemisphere coaxially aligned with and mounted in opposition to said lower hemisphere, said lower hemisphere and said upper hemisphere each having an equatorial surface forming a gap therebetween in which a ring shaped workpiece can be radially magnetized, said lower hemisphere and said upper hemisphere each having an inner surface which forms a spherical cavity in which an iron fill material may be disposed, and said lower hemisphere and said upper hemisphere each having a flux line pathway comprising an axial and a radial flux component within said cavity.
The use of a lower hemisphere and an upper hemisphere having respective flux pathways with coacting radial flux components avoids the problem of requiring a relatively high capacity power supply to produce a high capacity current.